The present invention relates to a refrigerating apparatus for use in an air conditioner or the like and, more particularly, to a refrigerant circuit thereof having a gas injection path.
A typical refrigerant circuit having a gas injection path is formed by connecting a compressor, a condenser, a first expansion device, a gas-liquid separator, a second expansion device and an evaporator successively through piping. In the thus formed refrigerant circuit, a piping is connected to the upper part of the gas-liquid separator, and the other end of the piping is connected and opened to an intermediate portion of a cylinder of the compressor, to form a gas injection path.
A high-pressure gas refrigerant discharged from the compressor flows into the condenser, where the gas refrigerant is cooled by a circulating fluid (air or water) and condensed to become a liquid refrigerant. The liquid refrigerant flowing out of the condenser passes through the first expansion device, where it is reduced to an intermediate pressure to allow a portion of the liquid refrigerant to gasify, and the gas and liquid portions of the refrigerant are separated through the gas-liquid separator. The liquid refrigerant flows out from the bottom part of the gas-liquid separator and passes through the second expansion device, where it is reduced to a predetermined pressure and then flows into the evaporator. In the evaporator, the liquid refrigerant absorbs heat from a circulating fluid (air or water) to evaporate, becoming a gas refrigerant, which returns to the compressor.
On the other hand, the gas refrigerant separated from the liquid refrigerant in the gas-liquid separator and collected in the upper part thereof is passed through the gas injection path and injected into the compressor during the compression stroke thereof.
In the case where a refrigerating apparatus having the above gas injection path is applied to a heat-pump type air conditioner, in the heating operation, the condenser serves as the service-side heat exchanger, while the evaporator serves as the heat source-side heat exchanger.
The refrigerant flowing into the gas-liquid separator through the first expansion device has about 20% to 30% gas refrigerant mixed therein. This gas refrigerant is separated in the gas-liquid separator and is then passed through the gas injection path and injected to the compressor during the compression stroke thereof. Accordingly, the amount of the refrigerant discharged from the compressor is larger, by the amount of the injected gas refrigerant, than that in the case where no gas injection is performed, so that the amount of heat given off in the condenser, i.e., the heating capacity increases.
On the other hand, in the air-cooling operation, the evaporator serves as the service-side heat exchanger, while the condenser serves as the heat source-side heat exchanger.
In the air-cooling operation, before the refrigerant flows into the evaporator, the gas refrigerant has already been separated therefrom in the gas-liquid separator, and only the liquid refrigerant, which is effective for heat exchange, flows into the evaporator. Accordingly, the amount of heat absorbed in the evaporator, i.e., the air-cooling capacity, increases.
As described above, the gas injection system has a refrigerant circuit that increases the heating or air-cooling capacity by injecting the gas refrigerant into the compressor during the compression stroke thereof. However, a conventional apparatus employing the gas injection system has the following problems. Since the gas refrigerant separated in the gas-liquid separator is constantly injected into the compressor during the compression stroke thereof, when the load on the apparatus increases, the discharge pressure and temperature excessively rise to lower the operation efficiency. In addition, the reliability is unfavorably lowered due to the rise in temperature of the electric motor unit incorporated in the compressor.
For overcoming the above-mentioned problems, means have been proposed wherein, in an overload operation such as mentioned above, the injection path is shut off and only the ordinary refrigerant circuit is employed.
In, for example, Japanese Patent Publication No. 47296/1980, a refrigerating apparatus is proposed wherein a stop valve is provided in an intermediate portion of the injection pipe interconnecting the gas-liquid separator and the compressor. The stop valve is open in the normal operation to inject the refrigerant gas, separated, in the gas-liquid separator into the compressor through the injection pipe and is closed, when the apparatus is started or overloaded, to shut off the injection pipe.
In, for example Japanese Utility Model Laid Open No. 104459/1976 a heat-pump type refrigerating apparatus is proposed wherein a stop valve is provided in an intermediate portion of the injection pipe interconnecting the gas-liquid separator and the compressor, and the stop valve is closed to shut off the injection pipe in an overload operation in which the discharge temperature is high or in the heating operation performed when the outside air temperature is high.
Both the of the above art apparatus are arranged such that, in an overload operation, the injection pipe is shut off to prevent the overheating of the compressor.
However, the load on the compressor cannot be reduced in a sufficient manner only by controlling the valve to open or close the gas injection path as in both the above-mentioned prior art apparatus. Moreover, if the injection path is shut off while the pressure reduction effected in the second expansion device is maintained constant, the liquid refrigerant collected in the gas-liquid separator and flowing out to the evaporator may be undesirably drawn into the compressor.
Accordingly, an object of the invention is to provide a refrigerating apparatus having a gas injection path and capable of checking the rise in discharge pressure and temperature by decreasing the amount of the refrigerant circulating through the refrigerant circuit when the load on the refrigerating apparatus increases.
To this end, according to the invention, a refrigerating apparatus comprises: a main refrigerant circuit constituted by a compressor, a condenser, a first expansion device, a gas-liquid separator, a second expansion device and an evaporator which are successively connected through piping, with an injection path interconnecting an upper part of the gas-liquid separator and a cylinder of the compressor during the compression stroke thereof. An auxiliary path is constituted by connecting a solenoid valve, closed in the normal operation, and an auxiliary expansion device, with the auxiliary path being provided between the gas-liquid separator and the evaporator so as to be parallel to the second expansion device. The auxiliary path is connected to the gas-liquid separator at a position higher than the connecting position of the second expansion device to the gas-liquid separator, wherein the solenoid valve is opened when the load on the refrigerating apparatus increases.
In the normal operation, the solenoid valve is closed, so that the refrigerant discharged from the compressor circulates through the main refrigerant circuit. In addition, the gas refrigerant separated in the gas-liquid separator is passed through the injection path and injected into the cylinder of the compressor during the compression stroke thereof. In such a normal operation, the amount of the refrigerant charged into the gas-liquid separator is set so that the level of the liquid refrigerant therein is relatively low.
When the load on the apparatus increases, the solenoid valve is opened. Consequently, the gas-phase part of the gas-liquid separator and the evaporator are allowed to communicate with each other through the auxiliary expansion device. Therefore, the difference in pressure between the gas-phase part and the evaporator decreases to reduce the amount of the liquid refrigerant collected in the gas-liquid separator and flowing out therefrom to the evaporator. As a result, the level of the liquid refrigerant in the gas-liquid separator gradually rises, i.e., the liquid refrigerant stored therein increases in amount, so that the refrigerant circulating through the refrigerant circuit decreases in amount. Accordingly, the refrigerant liquid collected in the condenser decreases in amount to lower the refrigerant supercooling degree at the outlet of the condenser. In addition, since the pressure in the gas-liquid separator lowers, the refrigerant injected into the compressor decreases in flow rate, and the refrigerant discharged from the compressor decreases in flow rate. Therefore, the rise in discharge pressure and temperature is prevented.
Another object of the invention is to provide a refrigerating apparatus capable of holding down the rise in discharge pressure and temperature to a smaller degree in an overload operation by decreasing the amount of the refrigerant circulating through the main refrigerant circuit as well as positively controlling the flow rate of the gas refrigerant to be injected.
To this end, according to the invention, the refrigerating apparatus, in addition to the above mentioned elements comprises a main flow path resistance member for controlling the flow rate provided in an intermediate portion of the injection path, and a path constituted by connecting through piping a solenoid valve for injection which is open in the normal operation and an auxiliary flow path resistance member. The path is connected in parallel to the main flow path resistance member, wherein, when the load on the refrigerating apparatus increases, the solenoid valve for the separator is opened and at the same time, the solenoid valve for injection is closed.
In the normal load condition, the operation of this refrigerating apparatus is similar to that of the first-mentioned refrigerating apparatus, except that the gas refrigerant to be injected into the compressor during the compression stroke thereof through the injection path flows through the main flow path resistance member and the auxiliary flow path resistance member in parallel.
When the load on the refrigerating apparatus is larger than normal, similarly to the first-mentioned refrigerating apparatus, the solenoid valve for the gas-liquid separator is opened to raise the level of the liquid refrigerant in the gas-liquid separator. Consequently, the refrigerant circulating through the refrigerant circuit decreases in amount. In addition, as the pressure in the gas-liquid separator lowers, the gas refrigerant to be injected into the compressor during the compression stroke thereof decreases in flow rate. Moreover, in this apparatus, the solenoid valve for injection is closed, so that the gas refrigerant to be injected flows through only the main flow path resistance member (the auxiliary flow path resistance member is shut off). As a result, the resistance to flow increases, so that the flow rate of the gas refrigerant to be injected is further decreased. Accordingly, the rise in discharge pressure can be held down to a smaller degree.
Thus, according to the invention, the amount of the refrigerant circulating through the refrigerant circuit and the flow rate of the gas refrigerant to be injected are regulated according to the load condition. Therefore, in the normal operation, the capacity and efficiency of the refrigerating apparatus can be increased by the gas injection. Moreover, when the load on the refrigerating apparatus increases, the rise in discharge pressure and temperature and the rise in input of the compressor can be held down to a small degree. Accordingly, the reliability can be increased through the improvement in operation efficiency and the prevention of overheating of the compressor.
The above and other objects, features and advantages of the invention will become clear from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.